The present invention relates to a magnetic memory capable of magneto-resistive reproduction of recorded information and a manufacturing method thereof, and in particular to a magnetic memory element in which stable magnetization exists in a storage layer despite high density, a magnetic memory and the manufacturing method thereof.
In recent years, an application of elements such as an Anisotropy Magneto Resistive (AMR) element, a Giant Magneto Resistive (GMR) element and a Magnetic Tunnel Junction (MTJ) element to an HDD reproducing head and a magnetic memory has been proposed. The magnetic memory, like a semiconductor memory, is a solid-state memory having no operation sections, and when compared to the semiconductor memory, the magnetic memory has a number of merits such that (a) it loses no information upon power-down, (b) it is available for the unlimited number of repeated use, and (c) it prevents the storage content thereof from being destroyed by an incident x-ray.
Particularly, the MTJ element can change to a large extent a resistance rate of change depending on directions of magnetization in a pair of ferromagnetic layers which form the MTJ element. The use of the MTJ element in a memory cell has been expected.
A structure of a conventional MTJ element is disclosed, for example, in Japanese Unexamined Patent Publication No. 106514/1997 (Tokukaihei 9-106514 published on Apr. 22, 1997).
A MTJ element 50, as shown in FIG. 33, is made up of an antiferromagnetic layer 51, a ferromagnetic layer 52, an insulating layer 53 and a ferromagnetic layer 54, which are stacked.
The antiferromagnetic layer 51 is made of an alloy such as FeMn, NiMn, PtMn and IrMn. The ferromagnetic layers 52 and 54 are made of Fe, Co or Ni, or an alloy thereof. Further, as a material of the insulating layer 53, the use of various oxides or nitrides has been examined, among which the use of an Al2O3 film is known to produce the highest magneto-resistive (MR) ratio.
Furthermore, other than the foregoing, there has been proposed a MTJ element which utilizes a difference in coercive force between the ferromagnetic layers 52 and 54 in a structure excluding the antiferromagnetic layer 51.
The principles of the MTJ element 50 when used as a magnetic memory are shown in FIG. 34.
Magnetization in both the ferromagnetic layers 52 and 54 is in-plane magnetization, which is subject to effective uniaxial magnetic anisotropy that directs magnetization either parallel or anti-parallel. In addition, magnetization of the ferromagnetic layer 52 is virtually fixed in one direction due to exchange coupling with the antiferromagnetic layer 51. Further, recording is retained in a direction of magnetization in the ferromagnetic layer 54 which flexibly varies within a range of the uniaxial magnetic anisotropy. Note that, xe2x80x9canti-parallelxe2x80x9d refers to a state of magnetization of the ferromagnetic layers 52 and 54 being parallel to each other and directed opposing each other.
The magnetization of the ferromagnetic layer 54 to be a storage layer has a characteristic that a resistance value of the entire MTJ element 50 varies according to which direction is taken, parallel or anti-parallel to the magnetization of the ferromagnetic layer 52.
Accordingly, when reproducing, the resistance value is detected so as to retrieve information data stored in the MTJ element 50.
Further, when recording, a magnetic field generated by a current wire disposed in a vicinity of the MTJ element 50 is utilized to change the direction of magnetization in the ferromagnetic layer 54, thereby performing writing of data to the MTJ element 50.
Meanwhile, the MTJ element 50 having the foregoing structure generates magnetic poles at both ends, since the ferromagnetic layers 52 and 54 are magnetized in the in-plane direction. As a result, when forming a memory array using the MTJ element 50, magnetostatic interaction occurs between the MTJ element 50 and an adjacent MTJ element. This means that a condition of the adjacent MTJ element has an effect on a characteristic of an individual MTJ element, thus making it difficult to reduce a spacing between the MTJ elements and increase a recording density.
In view of the foregoing problems, Japanese Unexamined Patent Publication No. 161919/1999 (Tokukaihei 11-161919 published on Jun. 18, 1999) discloses a method of reducing an effect of edge magnetic poles.
A structure of the MTJ element 60 which reduces the effect on the edge magnetic poles is shown in FIG. 35. In FIG. 34, a ferromagnetic layer (fixed layer) 62, the direction of magnetization is fixed by being coupled with an antiferromagnetic layer 61, and a ferromagnetic layer (flexible layer) 64 which can flexibly rotate with respect to an external magnetic field are stacked so as to sandwich an insulating layer 63. Furthermore, the ferromagnetic layer 62 has a structure such that a pair of ferromagnetic layers 71 and 73 which are antiferromagnetically coupled sandwich a non-magnetic metallic layer 72. Likewise, the ferromagnetic layer 64 has a structure such that a pair of ferromagnetic layers 74 and 76 which are antiferromagnetically coupled sandwich a non-magnetic metallic layer 75, thereby reducing magnetic poles generated on the edges of both the ferromagnetic layer 64 as the flexible layer and ferromagnetic layer 62 as the fixed layer.
However, the conventional magnetic memory as above has the following problems.
The ferromagnetic layer (flexible layer) 64 which does not adjoin the antiferromagnetic layer is composed of NiFe layer/Ru layer/NiFe layer, and flexibly rotates when an external magnetic field is applied. In the prior art document, non-magnetic metallic layer (Ru layer) 75 has a film the thickness of which is set so that the pair of ferromagnetic layers (NiFe layers) 74 and 76 have the maximum antiferromagnetic coupling strength and slightly different film thicknesses therebetween. When a magnetic field is applied from the outside, the ferromagnetic layer 64 as the flexible layer rotates net magnetization generated due to a difference between the film thicknesses of the pair of ferromagnetic layers (NiFe layers) 74 and 76.
However, a film thickness of the non-magnetic metallic layer (Ru layer) 75 is set so that the pair of ferromagnetic layers (NiFe layers) 74 and 76 have the maximum antiferromagnetic coupling strength therebetween. Therefore, the film thickness of the non-magnetic metallic layer (Ru layer) 75 ranges from 4 xc3x85 to 8 xc3x85, that is considerably thin. In this arrangement, formation of a pin hole works in reverse and induces ferromagnetic coupling, and it is thus difficult to obtain stable antiferromagnetic coupling strength. In addition, in order to allow an external magnetic field to reverse a direction of magnetization, the pair of ferromagnetic layers (NiFe layers) 74 and 76 are required to have different film thicknesses. More specifically, when apparent magnetization of the two layers is 0, it is difficult to reverse magnetization, and therefore, magnetization requires to be generated by changing a film thickness. However, a difference in the film thicknesses of the two layers prevents the net magnetization of the externally viewed MTJ element 60 from being reduced to zero. Accordingly, there has been a problem that the conventional magnetic memory cannot provide high-density magnetic memory because a magnetic pole which is generated on an edge of a ferromagnetic layer adversely affects an adjacent magnetic memory element.
Further, when using the MTJ element 60 as a magnetic memory element, a magnetic field which is required to reverse magnetization is generated by the passage of electric current through adjacent conductive wires. However, in the prior art document, no arrangements to reduce power consumption is disclosed.
Furthermore, in the conventional magnetic memory, when adopting the MTJ element 60 as a magnetic head, the MTJ element 60 is used in a state in which an applied magnetic field and the direction of an axis of hard magnetization of the ferromagnetic layer (flexible layer) 64 intersects at a right angle. However, when adopting the MTJ element 60 as a magnetic memory element, it is common that the magnetic field generated from two mutually intersecting conductive wires on the magnetic memory element rotates the magnetization of the ferromagnetic layer (flexible layer) 64. This causes an applied magnetic field to incline its direction to the direction of the axis of the hard magnetization of the ferromagnetic layer (flexible layer) 64. Consequently, it is unlikely that such a simple reversal of magnetization due to the rotation of magnetization as disclosed in the prior art document actually takes place, which prevents an element having this arrangement from being used as a magnetic memory element.
In view of the foregoing problems, it is an object of the present invention to provide (i) a magnetic memory element which is capable of maintaining stable magnetization stored in a storage layer, and low power consumption, (ii) a magnetic memory having this magnetic memory element, and (iii) a manufacturing method of the magnetic memory.
In order to solve the foregoing problems, the magnetic memory according to the present invention has a magnetic memory element including lamination of at least a first ferromagnetic layer, a non-magnetic layer and a second ferromagnetic layer, where a third ferromagnetic layer is provided via at least one conductor layer in-between, on one side of the second ferromagnetic layer the other side of which is closer to the non-magnetic layer.
Further, in order to solve the foregoing problems, the magnetic memory of the present invention includes a plurality of ferromagnetic layers having uniaxial anisotropic in-plane magnetization and an insulating layer on axes in parallel with each other, and utilizes a tunnel effect so as to reproduce magnetization information, and the magnetic memory further includes a first ferromagnetic layer as being a fixed layer and a second ferromagnetic layer as being a storage layer among the plurality of ferromagnetic layers; and a first conductor layer for supplying a current between the second ferromagnetic layer and a third ferromagnetic layer which flexibly reverses a direction of magnetization, wherein the first conductor layer supplies a current in a direction perpendicular to a direction of magnetization in the first ferromagnetic layer.
With the foregoing arrangement, magnetization information is stored in the magnetic memory when a current flowing through the first conductor layer applies a magnetic field to the second ferromagnetic layer as being a storage layer. Magnetization given to the second ferromagnetic layer as being the storage layer and magnetization given to the third ferromagnetic layer, which is formed on the opposite side via the first conductor layer in-between, cancel each other out in opposite directions. More specifically, to the second and third ferromagnetic layers located on and under the first conductor layer, respectively, are applied magnetic fields of opposite directions according to the corkscrew rule, thereby causing magnetization in the two ferromagnetic layers to face opposite directions. Thus, the magnetization in the second and third ferromagnetic layers cancel each other out, thereby reducing apparent magnetization in the magnetic memory element and therefore reducing a possible adverse effect over adjacent magnetic memories.
Accordingly, the magnetic memory elements can be disposed while reducing an interval therebetween, thereby realizing a magnetic memory having higher density than a conventional magnetic memory. Moreover, the first conductor layer, which supplies a current to provide magnetization information, may be provided in the vicinity of the second ferromagnetic layer as being the storage layer, thereby providing a magnetic memory capable of generation of a magnetic field sufficient for reversing magnetization even with a small current, and therefore low power consumption.
In order to solve the foregoing problems, a manufacturing method of the magnetic memory of the present invention which includes a plurality of magnetic memory elements having lamination of at least a first ferromagnetic layer, a non-magnetic layer and a second ferromagnetic layer as being a storage layer, the method including the steps of: forming a laminated film composed of at least the first ferromagnetic layer, the non-magnetic layer and the second ferromagnetic layer in this order from the side of a substrate successively on the substrate; processing the laminated film into the shape of each of the plurality of magnetic memory element which is separated from the others; forming an insulating layer so as to fill a spacing among the plurality of magnetic memory elements formed on the substrate; forming a conductor layer and a third ferromagnetic layer successively on the insulating layer provided over and between the plurality of magnetic memory elements; and processing the conductor layer so that the adjacent magnetic memory elements are coupled only in one direction, after processing the third ferromagnetic layer into substantially the same shape of each of the magnetic memory elements.
Further, in order to solve the foregoing problems, the manufacturing method of the magnetic memory has a plurality of magnetic memory elements having lamination of at least a first ferromagnetic layer, a non-magnetic layer and a second ferromagnetic layer as being a storage layer, the method including the steps of: forming a laminated film composed of at least the first ferromagnetic layer, the non-magnetic layer and the second ferromagnetic layer in this order from the side of a substrate successively on the substrate; processing the laminated film into the shape of each of the plurality of magnetic memory element which is separated from the others; forming an insulating layer so as to fill a spacing among the plurality of magnetic memory elements formed on the substrate; forming a first conductor layer and an insulating layer successively on the insulating layer provided over and between the plurality of magnetic memory elements; processing the first conductor layer so that the adjacent magnetic memory elements are coupled only in one direction; forming an insulating layer so as to fill a spacing around the processed first conductor layer; forming a second conductor layer and a third ferromagnetic layer successively on the insulating layer provided over and between the processed first conductor layer; and processing the second conductor layer so that the adjacent magnetic memory elements are coupled only in a direction orthogonally intersecting the first conductor layer, after processing the third ferromagnetic layer into substantially the same shape of the magnetic memory element.
Further, in order to solve the foregoing problems, a manufacturing method of the magnetic memory of the present invention which includes lamination of a plurality of ferromagnetic layers and an insulating layer, and a storage portion to store magnetization information, and detects a change in resistance in a current flowing through the storage portion according to a tunnel effect, the method including the steps of: forming a third ferromagnetic layer having uniaxial anisotropic in-plane magnetization on a substrate; forming a first conductor layer for supplying a current by being coupled with magnetic memory elements adjacent to each other in a direction orthogonally intersecting a direction of magnetization in said third ferromagnetic layer; forming an insulating layer so as to cover an upper surface of said first conductor layer and fill spacings among said magnetic memory elements; forming a third conductor layer as being a lower electrode for detecting said change in resistance; forming a storage portion including a ferromagnetic layer having uniaxial anisotropic in-plane magnetization, and an insulating layer on an axis parallel to magnetization in the third ferromagnetic layer; and forming a second conductor layer, as being an upper electrode which detects said change in resistance, for supplying a current by being coupled with the magnetic memory elements adjacently provided in a direction parallel to the direction of magnetization in said third ferromagnetic layer.
With the foregoing method, apparent magnetization in every magnetic memory element composing the magnetic memory can be made smaller than that of a conventional magnetic memory, thereby maintaining stable magnetization in the storage layer even in the magnetic memory having the magnetic memory elements closely disposed, thus attaining a magnetic memory with higher density than a conventional magnetic memory.
More specifically, magnetization information is stored in the magnetic memory in such a manner that a synthetic magnetic field of magnetic fields, one of which is generated from a current flowing through the first conductor layer and the other from a current flowing through the second conductor layer, is provided to the third ferromagnetic layer and a ferromagnetic layer which is a storage layer making up a storage portion.
The first conductor layer is located between the third ferromagnetic layer and the storage portion. Therefore, according to the corkscrew rule, the current flowing through the first conductor layer provides the third ferromagnetic layer and the storage portion with magnetic fields having directions opposite to each other. In addition, the second conductor layer is located at the top of lamination, thereby feeding a current in a direction parallel to the direction of magnetization in the first ferromagnetic layer. This makes a magnetic field given from the second conductor layer directed perpendicular to the direction of magnetization in the third ferromagnetic layer and the storage portion.
Furthermore, the third ferromagnetic layer and a ferromagnetic layer of the storage portion have in-plane magnetization which has parallel uniaxial anisotropy. Therefore, a synthetic magnetic field of the magnetic fields generated from currents flowing through the first and second conductor layers that was provided to the third ferromagnetic layer and the ferromagnetic layer of the storage portion turns to the opposite direction on one axis. As a result, magnetization in the third ferromagnetic layer and that in the ferromagnetic layer of the storage portion becomes anti-parallel. The magnetization information stored in the ferromagnetic layer of the storage portion is maintained until further magnetization information to be stored next is provided. Therefore, the second and third ferromagnetic layers remain in a state of canceling each other out in the magnetic memory element, thereby allowing the magnetic memory elements to individually have smaller apparent magnetization than a conventional magnetic memory element.
Accordingly, even when having a fine pattern by reducing an interval between the magnetic memory elements composing the magnetic memory, an adverse effect over adjacent magnetic memory elements becomes less feasible, thereby providing a magnetic memory with higher density.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.